• Energy Research

Abstract Adsorption heat storage (AHS) is an energy-saving technology that allows low-temperature heat from renewable energy sources and various wastes to be utilized. One of the most important ways to increase the efficiency of the AHS units is to develop adsorbents with high heat storage density. This work addresses the methanol sorption on an innovative composite based on expanded vermiculite impregnated with LiCl (LiCl/Verm), which is suggested for adsorptive cycles for seasonal heat storage. Such a cycle is typical of regions with moderately cold winter, like the South of the Russian Federation as well as the Northern part of China, Europe etc. The study consists of: (1) synthesis and characterization of the composite; (2) investigation of equilibrium and dynamics of methanol sorption under operating conditions of the seasonal AHS cycle; (3) evaluation of the sorbent heat storage capacity and specific power. The heat storage capacity of LiCl/Verm under conditions of the tested cycle reaches 1.5 kJ/g. This value far exceeds that for conventional and innovative adsorbents. The specific power of 0.9 and 1.5 kW/kg can be realized during discharging and charging stages of the cycle, respectively. These findings demonstrate a high potential of the LiCl/Verm composite as methanol sorbent for AHS.

Abstract Adsorption technologies for Heat Conversion (AHC) and Water Harvesting (AWH) hold great potential for energy management because they can utilize renewable energy or low-grade heat resources. A keystone for the successful implementation of these technologies is the properties of the adsorbent. Metal-organic frameworks (MOFs) show tremendous promise for these applications, owing to their high adsorption capacity and the possibility of target-specific design. However, there are several challenges to be solved, namely, low hydrothermal stability of MOFs, high cost, and complicated synthesis. The further progress of these technologies depends on the inter-disciplinary research in Applied Thermal Engineering (ATE) and Materials Science (MS) and close collaboration between these two scientific societies is required. In this review, we try to bridge the gap between ATE and MS scientists. To this purpose, the principles of AHC and AWH are described, the specific features of adsorbents needed for AHC and AWH are defined, and promising MOFs are considered. MOFs fabrication strategies and long-term reliability are viewed. Finally, we provide some perspectives on advanced MOFs promising for continuously-operating and scalable AHC and AWH systems.

Abstract Adsorption heat transformation (AHT) has attracted an increasing research interest as energy saving and environmentally benign alternative to vapor compression systems. Novel adsorbent NH 2 -MIL-125 could be promising for AHT owing to its high water adsorption capacity and good hydrothermal stability, although its dynamic properties have not been tested yet. In this paper the results of dynamic study of water adsorption on loose grains of NH 2 -MIL-125 are presented. The adsorption dynamics is studied by a Large Temperature Jump method under typical operating conditions of isobaric stages of adsorptive cooling cycle. The effects of the adsorption/ desorption temperature, adsorbent grain size and number of the grain layers are explored. The water adsorption on the grains of 0.2–1.8 mm size are shown to occur under at “grain size insensitive” mode as the adsorption rate is determined by the ratio S / m of the heat transfer area to the adsorbent mass regardless the grain size. Indeed, the ad/desorpion rate and the Specific Cooling Power (SCP) are proportional to the ( S / m )-ratio. Quite high SCP-values of 0.4–2.8 kW/kg can be obtained in adsorption chillers having a large ( S / m )-ratio of 1.6–6.9 m 2 /kg, which is of high practical interest.

A family of Composites “Salt inside Porous Matrix” (CSPM) has been considered as promising for adsorption heat transformation (AHT) due to their high sorption capacity, steep sorption isobars and opportunity to harmonize CSPM properties with boundary conditions of the AHT cycle. In this communication, we extend the harmonizing tools by confinement of one more salt to the matrix pores. Novel CSPMs based on a binary mixture of lithium, calcium, and barium halides inside various mesoporous matrices were synthesized with wide variation of the relative salts content. Their phase composition and sorption equilibrium with water, methanol and ammonia vapour were studied by XRD and TG techniques. It was shown that the formation of a homogeneous solid solution of the salts led to changing the equilibrium temperature (pressure) of the solvation. Thus, the confinement of binary salt systems to the matrix pores can be an effective tool for designing innovative materials with predetermined sorption properties adapted to particular AHT cycles.

In this study, the development and comparative characterization of different composite sorbents for thermal energy storage applications is reported. Two different applications were targeted, namely, low-temperature space heating (SH) and domestic hot water (DHW) provision. From a literature analysis, the most promising hygroscopic salts were selected for these conditions, being LiCl for SH and LiBr for DHW. Furthermore, two mesoporous silica gel matrixes and a macroporous vermiculite were acquired to prepare the composites. A complete characterization was performed by investigating the porous structure of the composites before and after impregnation, through N2 physisorption, as well as checking the phase composition of the composites at different temperatures through X-ray powder diffraction (XRD) analysis. Furthermore, sorption equilibrium curves were measured in water vapor atmosphere to evaluate the adsorption capacity of the samples and a detailed calorimetric analysis was carried out to evaluate the reaction evolution under real operating conditions as well as the sorption heat of each sample. The results demonstrated a slower reaction kinetic in the vermiculite-based composites, due to the larger size of salt grains embedded in the pores, while promising volumetric storage densities of 0.7 GJ/m3 and 0.4 GJ/m3 in silica gel-based composites were achieved for SH and DHW applications, respectively.

Adsorption heat transformation is an energy and environment saving technology for cooling/heating driven by renewable energy sources. Each specific cycle of adsorption heat transformer (AHT) makes particular requirements to the properties of the sorption material, depending on the climatic zone in which the AHT is used, the type of application (cooling, heating and heat storage), and energy source used for regenerating the sorbent. Therefore, the effective operation of AHT can be realized only if the working pair “adsorbent-adsorbate” is intelligently selected in accordance with the requirements of a particular working cycle. One of the most important factors influencing the choice of a working pair is the climatic conditions in which the AHT will operate. In this paper, the climatic conditions of various regions of Russian Federation (RF) were analyzed. For each considered zone, the boundary potentials of Polanyi corresponding to different AHT cycles are calculated. The sorption equilibrium data of vario...

Great current progress in the materials science offers an enormous choice of novel adsorbents which may be promising for transformation and storage of low temperature heat, e.g. from renewable heat sources. This paper gives an overview of recent trends and achievements in this field. We consider possible optimization of zeolites by dealumination, further development on aluminophosphates, composites “salt in porous host matrice” and metal-organic frameworks which are currently receiving the largest share of scientific attention. The particular attention is focused on the chemical nano-tailoring and tunable adsorption behavior of these materials to satisfy the demands of appropriate heat transformation cycles. We hope that this review will give new impact on target-oriented research on the novel adsorbents for heat transformation and storage.

Abstract With exhausting fossil fuels and increasing demand for heating and cooling, the effective utilization of renewable and waste energy sources becomes of increasing importance. Adsorption cooling driven by low temperature heat is an energy and environment saving alternative to the common compression systems. The performance of adsorption chillers strongly depends on the compliance of the adsorbent properties with the cycle operating conditions. In this paper, the comprehensive study of equilibrium and dynamics of water adsorption on a new efficient adsorbent of water vapour MOF-801 is performed to evaluate its feasibility for adsorption cooling. It was shown that at the adsorption temperature of 30 °C the MOF-801 provides the cooling effect at the evaporation temperature as low as 5 °C that indicates significant affinity to water vapour. On the other hand, it can be regenerated by low temperature heat at 80–85 °C. The uptake variation under the conditions of a typical adsorption cooling cycle reaches 0.21 g/g. Water adsorption on loose grains of MOF-801 occurs under grain-size insensitive mode when the adsorption rate is proportional to the (S/m)-ratio of the heat transfer surface S to the adsorbent mass m. The Specific Cooling Power equal to 2 kW/kg is measured at S/m = 6 m2/kg and 80% of reaching the equilibrium conversion, which is of high practical interest. Thus, the results obtained demonstrate the high potential of the working pair “MOF-801 – water” for adsorption cooling.

Abstract Development of new adsorbents of water and methanol specialised for AHT (adsorption heat transformation) can essentially advance this emerging low-carbon technology. This paper addresses the synthesis of novel composite sorbents based on an AA (anodic alumina) layer impregnated with hygroscopic salts, and the study of their ability to sorb water and methanol vapours. This work consists of the three parts: (1) synthesis and comparison of AA/Al sandwiches obtained with various electrolytes (sulphuric, oxalic, and phosphoric acids); (2) preparation of salt/AA composites (salt = CaCl 2 and LiCl) and study of their sorption equilibrium and dynamics with water and methanol vapours; and (3) evaluation of the new sorbents feasibility for AHT applications. The results obtained show that a) the new AA-based composites could be interesting for making compact AHT units with short working cycles, and b) still more R&D are necessary for further progress towards practical implementation of the new sorbents.